Very violent 2-3 shift flares after transmission builds. Happens on every unit so far

I've got a trans builder doing our transmissions that's been building GM transmissions for 40 years. Very experienced and reputable, but I am not so sure he knows what he's doing on 6L80's anymore. The last 6 units I've had him build all have a very nasty shift flare on the 2-3 that WAS NOT there before, and lots of uncomfortable clunking while downshifting coming to a stop. Also occasional 4-5 shift flares. A couple of these have been pulled and taken back for inspection only for the problem to show up again. I'll repeat, these cars did NOT have these issues before and I had the trans tuning dialed in quite nicely. The builds were done to hold more power.

So far I've played with shift times, shift intertia factor, TQ management, etc to no avail. Nothing changes it. Anyone have any experience with this and know a way to smooth it out without having to do tear downs all over again? We're using PATC parts throughout.

Thanks

Exuse my English.It trouble have link with pressure. Insufficient oncoming pressure during 2-3,3-4,4-5 UpShifts go to slip frictions and flare rpm. Increased torque (after charger be installed) without TCM tuning will cause flare too. TCM learning not always cope with the responsibilities. You need try work not only with oncoming,but offgoing and shift pressure and other things in ECM. I"ll try help you,what I could,if you need it.

That -Guy . mate post your tune so I can have a look at trans settings mate......Cheers Bret ULTIMATE LSX TUNING

Sounds like a tune issue. From the factory the 2-3 shift was shit due to seals or something of that sort. Might be now that it's been rebuild it's causing an issue .

Are you doing the relearn with a scan tool? all 6l80e's need to relearn clutch fill times after overhaul, due to different clearances after rebuild

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Originally Posted by That_guy

I've got a trans builder doing our transmissions that's been building GM transmissions for 40 years. Very experienced and reputable, but I am not so sure he knows what he's doing on 6L80's anymore. The last 6 units I've had him build all have a very nasty shift flare on the 2-3 that WAS NOT there before, and lots of uncomfortable clunking while downshifting coming to a stop. Also occasional 4-5 shift flares. A couple of these have been pulled and taken back for inspection only for the problem to show up again. I'll repeat, these cars did NOT have these issues before and I had the trans tuning dialed in quite nicely. The builds were done to hold more power.

So far I've played with shift times, shift intertia factor, TQ management, etc to no avail. Nothing changes it. Anyone have any experience with this and know a way to smooth it out without having to do tear downs all over again? We're using PATC parts throughout.

Thanks

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Ever figure this out?